1. Field of the Invention
The present invention relates to a local positioning apparatus for use in a local positioning system for providing local positioning data related to location, velocity, and posture of an object on the local ground and particularly suitable for detection of both the moving and stationary states of an automobile on the road.
2. Description of the Prior Art
In FIG. 30, a conventional local positioning apparatus used in an automobile is shown. The conventional local positioning system LPP includes an edge extractor 1P, a threshold generator 3P, a contour extractor 5P, a matching operator 9P, and a lane mark contour extractor 11P, a region limiter 13P, a current position detector 15P, a curvature detector 17P, and a yaw angle detector 19P.
The edge extractor 1 is connected to a digital imaging device 100 mounted on an automobile AM (FIG. 1) for obtaining a perspective view Vi of the object located in an advancing direction of the automobile AM. The edge extractor 1 receives the image signal Si indicating the advancing direction view Vi (FIG. 3) of the road surface wherein lane markings Lm1, Lm2, and Lm3 are applied. The edge extractor 1 extracts edge pixels from the signal Si and produces an extracted edge pixel signal Sx' indicative of an extracted edge view Vx' including edge pixels of the lane makings Lm.
The threshold generator 3P determines a threshold Eth' to extract the edge pixels around the contour of the image of the lane makings from the edge pixel data signal Sx' according to a known method. The contour extractor 5 scans the signal Sx' with respect to the threshold Eth' to extract a line of each lane marking Lm, and produces an extracted lane marking signal Sc'.
The matching operator 9P determines the straight or curved line matching the extracted lane contour line data Sc, and produces a matching signal Sm' including dimensional data of such matching lines. The lane mark contour extractor 11P extracts only the matching lines satisfying the possible dimensional features of lane marks on the road from the signal Sm' to produce an extracted lane signal Smc'.
Based on the extracted lane signal Smc', the region limiter 13P determines a region around each of the thus extracted lane marking lines having a predetermined area. Then, the region limiter 13P produces a region signal Sr' defining the regions.
Based on the region signal Sr', the edge extractor 1 limits the area to scan around the detected lane markings. The current position detector 15P detects the position with respect to the road on which the automobile AM is currently located. The curvature detector 17P obtains the curvature of the lane. The yaw angle detector 19P detects the tilting angle of the automobile with respect to the lane.
However, according to the perspective view, since the three-dimensional relationships are represented on a two-dimensional surface, the distant object is represented by a smaller size than the near object. The object's shape is distorted more depending on the distance remote from the imaging device 100 or the automobile AM.
Since the three-dimensional relationships are represented on a two-dimensional surface in the perspective view, the distant object is represented by a smaller size than the near object. In other words, an object in a position far from the automobile AM is expressed in a distorted shape more than that in a position nearby. Note that the images obtained by the signals Si, Sx', and Sc' operate to express the actual (true) shape of the object as a plan view for example.
It is impossible to obtain correct dimensional information of the object from the signal Sc' regardless the distance between the object and the imaging device 100. This clearly means that correct dimensional information of the road (lane) cannot be obtained, and much less the positional relationships between the automobile and the road.
Note that all positioning operation such as matching, lane contour extraction, current position detection, curvature detection, and yaw angle detection are performed based on such incorrect dimensional information included in the signal Sc. Apparently, positioning operation by the conventional local positioning apparatus LPP is incorrect, unreliable, and hazardous.
Another conventional local positioning apparatus is proposed in Japanese Laid-Open Patent Publication H3-139706. According to this conventional local positioning apparatus, an image of two lane marks for guiding an automobile is taken by an imaging device. Two tangent lines having different lengths are drawn to those two lane marks for calculating a curvature of the lane marks. Based on this calculated curvature and a relationship between a curvature and automobile conditions which are previously stored therein, the shifting distance in a lateral direction is obtained.
However, sometimes the lane has a curvature too small to detect correctly. Furthermore, when an interval between two lane markings varies, the conventional local positioning apparatus cannot function properly. As a result, a local position of the automobile on a road cannot be detected.